Poly(amide-imide) copolymer, method of manufacturing the same, poly(amide-imide) copolymer film, window for display device, and display device

ABSTRACT

A poly(amide-imide) copolymer including an amide structural unit having an amide bond in a polymer main chain and an imide structural unit having an imide bond in a polymer main chain, wherein at least one imide structural unit includes a moiety cross-linked to an adjacent polymer main chain through an amide bond.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2017-0023582 filed in the Korean Intellectual Property Office on Feb.22, 2017, and all the benefits accruing therefrom under 35 U.S.C. § 119,the content of which is incorporated herein in its entirety byreference.

BACKGROUND 1. Field

A poly(amide-imide) copolymer, a method of manufacturing the same, apoly(amide-imide) copolymer film, a window for a display device, and adisplay device are disclosed.

2. Description of the Related Art

To be manufactured into a smart phone, a tablet PC, or the like, aportable electronic device must include a display device that isflexible (for example, bendable, foldable, or rollable).

Currently, the display device mounted on the portable electronic deviceutilizes strong glass to protect a display module.

However, the glass lacks of flexibility, and thus may not be used in aflexible display device.

Accordingly, there is a need for a transparent film made of a polymermaterial as an alternative to the glass.

SUMMARY

An embodiment provides a poly(amide-imide) copolymer capable ofimproving optical characteristics and mechanical characteristics.

Another embodiment provides a method of manufacturing thepoly(amide-imide) copolymer.

Yet another embodiment provides a poly(amide-imide) copolymer filmcapable of improving optical characteristics and mechanicalcharacteristics.

Still another embodiment provides a window for a display deviceincluding the poly(amide-imide) copolymer film.

Further embodiment provides a display device including the window for adisplay device.

Further embodiment provides a poly(amide-imide) copolymer precursor forforming the poly(amide-imide)copolymer.

According to an embodiment, a poly(amide-imide) copolymer includes:

an amide structural unit having an amide bond included in a polymer mainchain, and

an imide structural unit having an imide bond included in the polymermain chain,

wherein at least one imide structural unit includes at least one moietycross-linked to an adjacent polymer main chain through an amide bond.

The imide structural unit may include:

a first imide structural unit including a moiety cross-linked to anadjacent polymer main chain through an amide bond, and

a second imide structural unit, which is not cross-linked to an adjacentpolymer main chain.

The first imide structural unit may include at least one of a structuralunit represented by Chemical Formula 1 and a structural unit representedby Chemical Formula 2.

In Chemical Formula 1 or 2,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain.

The structural unit represented by Chemical Formula 1 may include astructural unit represented by Chemical Formula 1a.

In Chemical Formula 1a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

The structural unit represented by Chemical Formula 1a may include atleast one of a structural unit represented by Chemical Formula 1aa and astructural unit represented by Chemical Formula 1ab.

The structural unit represented by Chemical Formula 2 may include astructural unit represented by Chemical Formula 2a.

In Chemical Formula 2a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

The structural unit represented by Chemical Formula 2a may include atleast one of a structural unit represented by Chemical Formula 2aa and astructural unit represented by Chemical Formula 2ab.

The second imide structural unit may include a structural unitrepresented by Chemical Formula 3.

In Chemical Formula 3,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain.

The second imide structural unit may include a structural unitrepresented by Chemical Formula 3a.

In Chemical Formula 3a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

The second imide structural unit may include at least one of astructural unit represented by Chemical Formula 3a and a structural unitrepresented by Chemical Formula 3b.

In Chemical Formulae 3aa and 3ab,

* is a linking point of the polymer main chain.

The amide structural unit may include a structural unit represented byChemical Formula 4.

In Chemical Formula 4,

L is the same or different in each structural unit and is independentlya single bond, —CONH—, -Ph-CONH-Ph-, or —NHCO-Ph-CONH—, wherein “Ph” isa substituted or unsubstituted phenylene group,

R² is the same or different in each structural unit and is independentlya divalent organic group including a substituted or unsubstituted C6 toC30 aromatic or non-aromatic ring, wherein the aromatic or non-aromaticring is present as a single ring; two or more aromatic or non-aromaticrings are condensed to provide a condensed polycyclic aromatic orcondensed polycyclic non-aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(k)(OH), SiR^(l)R^(m), or(CR^(n)R^(o))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic or non-condensed polycyclic non-aromatic group, wherein R^(k)to R^(o) are independently hydrogen, a C1 to C30 alkyl group, a C1 toC30 haloalkyl group, a halogen, or a hydroxy group,

R⁶ to R⁹ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n3 and n4 are the same or different in each structural unit and areindependently an integer ranging from 0 to 4,

n5 and n6 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3,

n3+n5 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4,

n4+n6 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4, and

* is a linking point of the polymer main chain.

The amide structural unit may include at least one of a structural unitrepresented by Chemical Formula 4a and a structural unit represented byChemical Formula 4b.

In Chemical Formulae 4a and 4b, * is a linking point of the polymer mainchain.

According to another embodiment, a poly(amide-imide) copolymer filmincludes the poly(amide-imide) copolymer.

The poly(amide-imide) copolymer film may satisfy a modulus of greaterthan or equal to about 5.8 gigapascals.

The poly(amide-imide) copolymer film may have a light transmittance ofgreater than or equal to about 80% and a yellow index of less than orequal to about 4.5.

According to another embodiment, a window for a display device includesthe poly(amide-imide) copolymer.

According to another embodiment, a display device includes the windowfor a display device.

According to another embodiment, a display device includes thepoly(amide-imide) copolymer film.

According to another embodiment, a poly(amide-imide) copolymer precursorincludes a poly(amide-amic acid) copolymer including an amide structuralunit and an amic acid structural unit included in a polymer main chain,and a diisocyanate.

The amic acid structural unit may include a structural unit representedby Chemical Formula 5 and the diisocyanate may be represented byChemical Formula 6.

In Chemical Formula 5,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain,OCN—Y—NCO  Chemical Formula 6

wherein, in Chemical Formula 6,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof.

The amide structural unit may include the structural unit represented byChemical Formula 4.

In Chemical Formula 4,

L is the same or different in each structural unit and is independentlya single bond, —CONH—, -Ph-CONH-Ph-, or —NHCO-Ph-CONH—, wherein “Ph” isa substituted or unsubstituted phenylene group,

R² is the same or different in each structural unit and is independentlya divalent organic group comprising a substituted or unsubstituted C6 toC30 aromatic or non-aromatic ring, wherein the aromatic or non-aromaticring is present as a single ring; two or more aromatic or non-aromaticrings are condensed to provide a condensed polycyclic aromatic orcondensed polycyclic non-aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond or a linking groupcomprising a substituted or unsubstituted fluorenyl group, O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(k)(OH), SiR^(l)R^(m),or)(CR^(n)R^(o))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic or non-condensed polycyclic non-aromatic group, wherein R^(k)to R^(o) are independently hydrogen, a C1 to C30 alkyl group, a C1 toC30 haloalkyl group, a halogen, or a hydroxy group,

R⁶ to R⁹ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n3 and n4 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4,

n5 and n6 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3,

n3+n5 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4,

n4+n6 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4, and

* is a linking point of the polymer main chain.

According to another embodiment, a method of manufacturing apoly(amide-imide) copolymer includes:

preparing a poly(amide-amic acid) copolymer including an amidestructural unit and an amic acid structural unit included in a polymermain chain,

reacting the poly(amide-amic acid) copolymer with the diisocyanate toprepare a poly(amide-imide) copolymer precursor including a moietycross-linked to an adjacent polymer main chain through an amide bond,and

imidizing the poly(amide-imide) copolymer precursor to obtain apoly(amide-imide) copolymer.

Optical characteristics and mechanical characteristics of the polymerfilm prepared from the above poly(amide-imide) copolymer may beimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, advantages and features of this disclosurewill become more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a cross-sectional view of a display device according to anembodiment, and

FIG. 2 is a cross-sectional view of a display device according toanother embodiment.

DETAILED DESCRIPTION

Exemplary embodiments will hereinafter be described in detail, and maybe readily performed by a person having an ordinary skill in the art.

However, this disclosure may be embodied in many different forms andshould not be construed as limited to the exemplary embodiments setforth herein.

Accordingly, the embodiments are merely described below, by referring tothe figures, to explain aspects of the present description. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. The term “or” means “and/or.”Expressions such as “at least one of” when preceding a list of elements,modify the entire list of elements and do not modify the individualelements of the list.

It will be understood that when an element is referred to as being “on”another element, it may be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer, or section.Thus, a first element, component, region, layer, or section discussedbelow could be termed a second element, component, region, layer, orsection without departing from the teachings of the present embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this general inventive conceptbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure, and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

“Mixture” as used herein is inclusive of all types of combinations,including blends, alloys, solutions, and the like.

As used herein, when a definition is not otherwise provided, the term“substituted” refers to replacement of a hydrogen atom of a compound bya substituent selected from a halogen atom, a hydroxy group, an alkoxygroup, a nitro group, a cyano group, an amino group, an azido group, anamidino group, a hydrazino group, a hydrazono group, a carbonyl group, acarbamyl group, a thiol group, an ester group, a carboxyl group or asalt thereof, a sulfonic acid group or a salt thereof, a phosphoric acidor a salt thereof, a C1 to C20 alkyl group, a C1 to C20 haloalkyl group,a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 arylgroup, a C7 to C30 arylalkyl group, a C1 to C30 alkoxy group, a C1 toC20 heteroalkyl group, a C3 to C20 heteroarylalkyl group, a C3 to C30cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15cycloalkynyl group, a C3 to C30 heterocycloalkyl group, and acombination thereof.

When a group containing a specified number of carbon atoms issubstituted with any of the groups listed in the preceding paragraph,the number of carbon atoms in the resulting “substituted” group isdefined as the sum of the carbon atoms contained in the original(unsubstituted) group and the carbon atoms (if any) contained in thesubstituent. For example, when the term “substituted C1 to C30 alkyl”refers to a C1 to C30 alkyl group substituted with C6 to C30 aryl group,the total number of carbon atoms in the resulting aryl substituted alkylgroup is C7 to C60.

As used herein, when a definition is not otherwise provided, “hetero”refers to inclusion of one to four heteroatoms selected from N, O, S,Si, and P.

Hereinafter, “combination” refers to a mixture of two or more and alaminate of two or more.

Hereinafter, “imide” refers to imide by itself and refers to imide andamic acid that is a precursor of the imide.

As used herein, the term “alkyl” indicates a group derived from acompletely saturated, branched or unbranched (or a straight or linear)hydrocarbon and having a specified number of carbon atoms.

As used herein, the term “haloalkyl” indicates an alkyl groupsubstituted with one or more halogen atoms selected from fluorine,chlorine, bromine, and iodine, wherein the term “alkyl” has the samemeaning as described above.

As used herein, the term “alkoxy” represents “alkyl-O—”, wherein theterm “alkyl” has the same meaning as described above.

As used herein, the term “alkenyl group” indicates a straight orbranched chain, monovalent hydrocarbon group having at least onecarbon-carbon double bond.

As used herein, the term “alkynyl group” indicates a straight orbranched chain, monovalent hydrocarbon group having at least onecarbon-carbon triple bond.

As used herein, when a definition is not otherwise provided, the term“aryl” indicates an aromatic hydrocarbon containing at least one ringand having the specified number of carbon atoms.

As used herein, the term “arylalkyl” indicates a substituted orunsubstituted aryl group covalently linked to an alkyl group that islinked to a compound.

As used herein, when a definition is not otherwise provided, the term“heteroaryl group” indicates an aryl group including carbon and 1 to 3heteroatoms selected from the group consisting of N, O, S, and P as ringatoms.

As used herein, the term “heteroarylalkyl” indicates a substituted orunsubstituted heteroaryl group covalently linked to an alkyl group thatis linked to a compound.

As used herein, the term “alkylene” indicates a straight or branchedsaturated aliphatic hydrocarbon group having a valence of at least two,optionally substituted with one or more substituents where indicated,provided that the valence of the alkylene group is not exceeded.

As used herein, the term “cycloalkylene group” indicates a cyclichydrocarbon group having a valence of at least two, optionallysubstituted with one or more substituents where indicated, provided thatthe valence of the cycloalkylene group is not exceeded.

As used herein, when a definition is not otherwise provided, the term“arylene” indicates a divalent group formed by the removal of twohydrogen atoms from one or more rings of an arene, wherein the hydrogenatoms may be removed from the same or different rings of the arene.

As used herein, the term “heteroarylene group” indicates a functionalgroup having a valence of at least two obtained by removal of twohydrogens in an aromatic ring, containing one to three heteroatomsselected from the group consisting of N, O, S, Si, and P as ring-formingelements, optionally substituted with one or more substituents whereindicated, provided that the valence of the alkylene group is notexceeded.

Hereinafter, a poly(amide-imide) copolymer according to an embodiment isdescribed.

A poly(amide-imide) copolymer according to an embodiment may be acopolymer having a main chain including at least one imide structuralunit and at least one amide structural unit in the polymer main chain.

At least one imide structural unit may be the same or different and eachimide structural unit may have an imide bond (—C(O)—NH—C(O)—) includedin the polymer main chain.

At least one amide structural unit may be the same or different and eachamide structural unit may have an amide bond (—C(O)—NH—) included in apolymer main chain.

The adjacent polymer main chains of the poly(amide-imide) copolymer maybe cross-linked, for example, through an amide bond (a bond between C(O)and NH in the amide bond —C(O)—NH—).

For example, at least one of the imide structural units of thepoly(amide-imide) copolymer may include a moiety cross-linked to anadjacent polymer main chain through an amide bond.

For example, the imide structural unit of the poly(amide-imide)copolymer may include:

a first imide structural unit including a moiety cross-linked to anadjacent polymer main chain through an amide bond, and

a second imide structural unit, which is not cross-linked to an adjacentpolymer main chain.

The first imide structural unit may include, for example, at least oneof a structural unit represented by Chemical Formula 1 and a structuralunit represented by Chemical Formula 2.

In Chemical Formula 1 or 2,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain.

For example, in Chemical Formula 1 and/or 2, X is the same or differentin each structural unit and is independently substituted orunsubstituted benzene, a substituted or unsubstituted naphthalene, asubstituted or unsubstituted anthracene, a substituted or unsubstitutedphenanthrene, a substituted or unsubstituted pyrene, a substituted orunsubstituted benzopyrene, a substituted or unsubstituted perylene, asubstituted or unsubstituted biphenylene, a substituted or unsubstitutedbridged biphenylene, a substituted or unsubstituted 5-membered or6-membered heterocycle, a substituted or unsubstituted cycloalkane, asubstituted or unsubstituted bridged bicycloalkane, a fused ringthereof, or a combination thereof, but is not limited thereto.

Herein the bridged biphenylene and the bridged bicycloalkane may belinked by, for example, a fluorenylene group or a linking groupincluding O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (wherein, R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group, 1≤p≤10), but are not limitedthereto.

For example, in Chemical Formula 1 and/or 2, X may be selected fromgroups of Group 1, but is not limited thereto.

Group 1

For example, in Chemical Formula 1 and/or 2, Y may be the same ordifferent in each structural unit and may independently be a substitutedor unsubstituted C1 to C20 alkylene group, a substituted orunsubstituted phenylene group, a substituted or unsubstitutednaphthylene group, a substituted or unsubstituted biphenylene group, ora combination thereof, but is not limited thereto.

For example, in Chemical Formula 1 and/or 2, R¹¹ may be the same ordifferent in each structural unit and may independently be selected fromgroups of Group 2, but is not limited thereto.

Group 2

For example, the first imide structural unit represented by ChemicalFormula 1 may include, for example, a structural unit represented byChemical Formula 1a.

In Chemical Formula 1a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

For example, the first imide structural unit represented by ChemicalFormula 1a may include, for example, at least one of a structural unitrepresented by Chemical Formula 1aa and a structural unit represented byChemical Formula 1ab, but is not limited thereto.

For example, the first imide structural unit represented by ChemicalFormula 2 may include, for example, a structural unit represented byChemical Formula 2a.

In Chemical Formula 2a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(e), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

For example, the first imide structural unit represented by ChemicalFormula 2a may include, for example, at least one of a structural unitrepresented by Chemical Formula 2aa and a structural unit represented byChemical Formula 2ab, but is not limited thereto.

The second imide structural unit may include, for example, a structuralunit represented by Chemical Formula 3.

In Chemical Formula 3,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain.

For example, in Chemical Formula 3, X may be the same or different ineach structural unit and is independently substituted or unsubstitutedbenzene, a substituted or unsubstituted naphthalene, a substituted orunsubstituted anthracene, a substituted or unsubstituted phenanthrene, asubstituted or unsubstituted pyrene, a substituted or unsubstitutedbenzopyrene, a substituted or unsubstituted perylene, a substituted orunsubstituted biphenylene, a substituted or unsubstituted bridgedbiphenylene, a substituted or unsubstituted 5-membered or 6-memberedheterocycle, a substituted or unsubstituted cycloalkane, a substitutedor unsubstituted bridged bicycloalkane, a fused ring thereof, or acombination thereof, but is not limited thereto.

Herein the bridged biphenylene and the bridged bicycloalkane may belinked by, for example, a fluorenylene group or a linking groupincluding O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (wherein, R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group, 1≤p≤10), but are not limitedthereto.

For example, the second imide structural unit represented by ChemicalFormula 3 may include, for example, a structural unit represented byChemical Formula 3a.

In Chemical Formula 3a,

R¹⁰ is the same or different in each structural unit and isindependently a single bond or a linking group including a fluorenylenegroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH),SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) areindependently hydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkylgroup, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup,

R¹² and R¹³ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n7 and n8 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3, and

* is a linking point of the polymer main chain.

For example, the second imide structural unit represented by ChemicalFormula 3a may include, for example, at least one of a structural unitrepresented by Chemical Formula 3aa and a structural unit represented byChemical Formula 3ab, but is not limited thereto.

In Chemical Formulae 3aa and 3ab, * is a linking point of the polymermain chain.

The first imide structural unit and the second imide structural unit maybe included in a mole ratio of about 1:99 to about 99:1.

Within the above range, the first imide structural unit and the secondimide structural unit may be, for example, included in a mole ratio ofabout 5:95 to about 95:5 or about 10:90 to about 90:10.

The amide structural unit of the poly(amide-imide) copolymer mayinclude, for example, a structural unit represented by Chemical Formula4.

In Chemical Formula 4,

L is the same or different in each structural unit and is independentlya single bond, —CONH—, -Ph-CONH-Ph- or —NHCO-Ph-CONH—, wherein “Ph” is asubstituted or unsubstituted phenylene group,

R² is the same or different in each structural unit and is independentlya divalent organic group including a substituted or unsubstituted C6 toC30 aromatic or non-aromatic ring, wherein the aromatic or non-aromaticring is present as a single ring; two or more aromatic or non-aromaticrings are condensed to provide a condensed polycyclic aromatic orcondensed polycyclic non-aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(k)(OH), SiR^(l)R^(m), or(CR^(n)R^(o))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic or non-condensed polycyclic non-aromatic group, wherein R^(k)to R^(o) are independently hydrogen, a C1 to C30 alkyl group, a C1 toC30 haloalkyl group, a halogen, or a hydroxy group,

R⁶ to R⁹ are the same or different in each structural unit and areindependently a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C1 to C30 haloalkyl group, a substituted orunsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstitutedC1 to C30 alkoxy group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heterocyclic group, asubstituted or unsubstituted silyl group, a halogen, a cyano group, ahydroxy group, a nitro group, or a combination thereof,

n3 and n4 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4,

n5 and n6 are the same or different in each structural unit and areindependently an integer ranging from 0 to 3,

n3+n5 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4,

n4+n6 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4, and

* is a linking point of the polymer main chain.

For example, the amide structural unit represented by Chemical Formula 4may include, for example, at least one of a structural unit representedby Chemical Formula 4a and a structural unit represented by ChemicalFormula 4b, but is not limited thereto.

In Chemical Formulae 4a and 4b, * is a linking point of the polymer mainchain.

In the poly(amide-imide) copolymer according to an embodiment, the imidestructural unit and the amide structural unit may be, for example,included in a mole ratio of about 10:90 to about 90:10.

Within the above range, the imide structural unit and the amidestructural unit may be, for example, included in a mole ratio of about10:90 to about 70:30 or about 10:90 to about 50:50.

The poly(amide-imide) copolymer according to an embodiment may beobtained from a poly(amide-imide) copolymer precursor.

A poly(amide-imide) copolymer precursor according to an embodiment mayinclude a poly(amide-amic acid) copolymer and a diisocyanate.

The poly(amide-amic acid) copolymer may include an amide structural unitand an amic acid structural unit included in a polymer main chain.

The amide structural unit is the same as above and may include, forexample, the structural unit represented by Chemical Formula 4.

The amic acid structural unit may include, for example, a structuralunit represented by Chemical Formula 5.

In Chemical Formula 5,

X is the same or different in each structural unit and is independentlya substituted or unsubstituted C6 to C20 monocyclic aromatic group, asubstituted or unsubstituted C4 to C20 monocyclic non-aromatic group, asubstituted or unsubstituted C8 to C20 condensed polycyclic aromaticgroup, a substituted or unsubstituted C6 to C20 condensed polycyclicnon-aromatic group, a substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 non-condensed polycyclic non-aromatic group, or a combinationthereof, wherein each of the substituted or unsubstituted C6 to C20non-condensed polycyclic aromatic group and the substituted orunsubstituted C6 to C20 non-condensed polycyclic non-aromatic group arelinked by a single bond, a substituted or unsubstituted fluorenyl group,or a linking group including O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group,

R¹¹ is the same or different in each structural unit and isindependently a single bond or a divalent organic group including asubstituted or unsubstituted C6 to C30 aromatic or non-aromatic ring,wherein the aromatic or non-aromatic ring is present as a single ring;two or more aromatic or non-aromatic rings are condensed to provide acondensed polycyclic aromatic group; or two or more aromatic ornon-aromatic rings are linked by a single bond, a substituted orunsubstituted fluorenyl group, or a linking group of O, S, C(═O),OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h), or(CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and

* is a linking point of the polymer main chain.

The diisocyanate may be, for example, represented by Chemical Formula 6.OCN—Y—NCO  Chemical Formula 6

In Chemical Formula 6,

Y is the same or different in each structural unit and is independentlya substituted or unsubstituted C1 to C20 alkylene group, a substitutedor unsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof.

For example, the diisocyanate may be an alkylene diisocyanate such ashexamethylene diisocyanate, toluene diisocyanate,isophoronediisocyanate, or a combination thereof, but is not limitedthereto.

The diisocyanate may be included in an amount of less than or equal toabout 200 mole percent (mol %) based on the total amount of theanhydride used for preparation of the poly(amide-imide) copolymerprecursor.

While not wishing to be bound by theory, it is understood that withinthe above range, optical characteristics and mechanical characteristicsof the poly(amide-imide) copolymer may be further effectively achieved.

Within the above range, the diisocyanate may be included in an amount ofabout 0.1 mol % to about 150 mol %, about 1 mol % to about 100 mol %,about 1 mol % to about 50 mol %, or about 1 mol % to about 10 mol %, butis not limited thereto.

The poly(amide-imide) copolymer may be, for example, manufactured by:

preparing a poly(amide-amic acid) copolymer,

reacting the poly(amide-amic acid) copolymer with the diisocyanate toprepare a poly(amide-imide) copolymer precursor including a moietycross-linked to an adjacent polymer main chain through an amide bond,and

imidizing the poly(amide-imide) copolymer precursor to obtain apoly(amide-imide) copolymer.

The poly(amide-amic acid) copolymer may be obtained by reacting ananhydride, a diamine compound, and a dicarboxylic acid derivative.

For example, the poly(amide-amic acid) copolymer may be obtained byfirst reacting a dicarboxyl derivative with a diamine compound to forman amide structural unit, adding an anhydride thereto, and reacting themto link an amide structural unit with an amic acid structural unit andto obtain the poly(amide-amic acid) copolymer.

For example, the poly(amide-amic acid) copolymer may be obtained byfirst reacting a dicarboxyl derivative with a diamine compound to obtainan oligomer (hereinafter, “amide oligomer”) including an amide group andamino groups at both terminal ends, and reacting the amide oligomer as adiamine compound with an anhydride to obtain the poly(amide-amic acid)copolymer.

For example, the poly(amide-amic acid) copolymer may be obtained byreacting an anhydride, a diamine compound, and a dicarboxylic acidderivative.

The anhydride may be, for example, tetracarboxylic acid dianhydride, forexample, tetracarboxylic acid dianhydride represented by ChemicalFormula 7, but is not limited thereto.

In Chemical Formula 7, R¹⁰, R¹², R¹³, n7, and n8 are the same asdescribed above.

The anhydride may be, for example, 2,3,3′,4′-biphenyltetracarboxylicdianhydride, 2,3,3′,4′-diphenylsulfone tetracarboxylic dianhydride,3,4′-oxydiphthalic anhydride, 3,3′,4,4′-biphenyltetracarboxylicdianhydride (BPDA), bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylicdianhydride, 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA),4,4′-oxydiphthalic anhydride, pyromellitic dianhydride, and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride, or a combination thereof, but is not limited thereto.

The diamine compound may be, for example, represented by ChemicalFormula 8, but is not limited thereto.

In Chemical Formula 8, L, R⁶ to R⁹, and n3 to n6 are the same asdescribed above.

The diamine compound may be, for example,2,2′-bis(trifluoromethyl)benzidine (TFDB), but is not limited thereto.

The dicarboxylic acid derivative may be, for example, represented byChemical Formula 9, but is not limited thereto.X¹—CO—R²—CO—X²  Chemical Formula 9

In Chemical Formula 9,

R² is the same as described above and X¹ and X² are independently ahalogen.

The dicarboxylic acid derivative may be, for example, 4,4′-biphenyldicarbonyl chloride (BPCL), terephthaloyl chloride (TPCL), or acombination thereof, but is not limited thereto.

The poly(amide-imide) copolymer precursor may be obtained by mixing thepoly(amide-amic acid) copolymer with the diisocyanate.

The diisocyanate may be included in an amount of less than or equal toabout 200 mol % based on the total amount of the anhydride used forpreparation of the poly(amide-imide) copolymer precursor.

Within the above range, it may be, for example, included in an amount ofabout 0.1 mol % to about 200 mol %, about 0.1 mol % to about 150 mol %,about 1 mol % to about 100 mol %, about 1 mol % to about 50 mol %, orabout 1 mol % to about 10 mol %, but is not limited thereto.

Within these ranges, optical characteristics and mechanicalcharacteristics of the poly(amide-imide) copolymer may be furthereffectively satisfied.

The poly(amide-imide) copolymer precursor may further include a reactioncatalyst.

The reaction catalyst is not particularly limited and may be, forexample, a tertiary amine compound, such as triethylamine, but is notlimited thereto.

The reacting may be carried out in a solvent, which may be an aproticpolar solvent. The aprotic polar solvent may include asulfoxide-containing solvent such as dimethylsulfoxide (DMSO) anddiethylsulfoxide, a formamide-containing solvent such as N,N-dimethylformamide (DMF) and N,N-diethylformamide, an acetamide-containingsolvent such as N,N-dimethylacetamide (DMA),N,N-dimethylmethoxyacetamide, and N,N-diethylacetamide, apyrrolidone-containing solvent such as N-methyl-2-pyrrolidone (NMP),N-acetyl-2-pyrrolidone, and N-vinyl-2-pyrrolidone, a phenol-containingsolvent such as phenol, o-cresol, m-cresol, p-cresol, xylenol,halogenated phenol, and catechol, hexamethylphosphoramide,γ-butyrolactone, tetrahydrothiophene dioxide, N-methyl-δ-caprolactam,N,N,N′,N′-tetramethylurea, or a mixture thereof. However, thisdisclosure is not limited to an aprotic polar solvent, and an aromatichydrocarbon solvent such as xylene or toluene may be used.

The imidizing of the poly(amide-imide) copolymer precursor may be, forexample, performed by heat treating at about 200° C. to about 500° C.,for example, about 250° C. to about 400° C., for several seconds toseveral minutes, but is not limited thereto.

The poly(amide-imide copolymer) may be prepared in a film form.

The poly(amide-imide copolymer) film may have, for example, a thicknessof about 20 micrometers (μm) to about 200 μm.

Within this range, the poly(amide-imide copolymer) film may have athickness of about 30 μm to about 150 μm or about 30 μm to about 100 μm.

The poly(amide-imide copolymer) film may be, for example, a transparentfilm.

The poly(amide-imide copolymer) film may have, for example, a lighttransmittance of greater than or equal to about 80% in a visible rayregion of about 380 nanometers (nm) to about 780 nm.

Within this range, the poly(amide-imide copolymer) film may have a lighttransmittance of greater than or equal to about 85%.

The poly(amide-imide copolymer) film may have, for example, a yellowindex (YI) of less than or equal to about 4.5 (absolute value).

Within this range, the poly(amide-imide copolymer) film may have, forexample, a yellow index of less than or equal to about 4.0 (absolutevalue) or less than or equal to about 3.5.

Herein the yellow index may be measured according to ASTM D1925standard.

The poly(amide-imide copolymer) film may have, for example, a haze ofless than or equal to about 1.0.

Within this range, the poly(amide-imide copolymer) film may have a hazeof less than or equal to about 0.8.

The poly(amide-imide copolymer) film may have, for example, a modulus ofgreater than or equal to about 5.8 gigapascals (GPa).

Within this range, the poly(amide-imide copolymer) film may have, forexample, a modulus of greater than or equal to about 6.0 GPa.

Within this range the poly(amide-imide copolymer) film may have, forexample, a modulus of about 5.8 GPa to 10 GPa or about 6.0 GPa to about10 GPa.

While not wishing to be bound by theory, it is understood that thepoly(amide-imide copolymer) film may improve mechanical characteristicsdue to the modulus included within these ranges.

The poly(amide-imide copolymer) film may have, for example, a pencilhardness of greater than or equal to about 2H.

Herein the pencil hardness is measured according to ASTM D3363.

The poly(amide-imide copolymer) film may be used in any object requiringtransparency and may be, for example, effectively used as a transparentsubstrate, a transparent protective layer, a transparent insulationlayer, or a window for a display device.

Hereinafter, the poly(amide-imide) film used as a window for a displaydevice is described.

FIG. 1 is a cross-sectional view showing a display device according toan embodiment.

Referring to FIG. 1, a display device 100 according to an embodimentincludes a display panel 50 and a window 30.

The display panel 50 may be, for example, an organic light emittingpanel or a liquid crystal panel, for example, a bendable display panel,a foldable display panel, or a rollable display panel.

The window 30 may be the poly(amide-imide) copolymer film and may bedisposed toward an observer side.

Another layer may be disposed between the display panel 50 and thewindow 30, and for example, a single layer or plural layers of polymerlayer (not shown) and/or a transparent adhesive layer (not shown) may befurther included.

FIG. 2 is a cross-sectional view showing a display device according toanother embodiment.

Referring to FIG. 2, a display device according to the presentembodiment includes a display panel 50, a window 30, and a touch screenpanel 70.

The display panel 50 may be, for example, an organic light emittingpanel or a liquid crystal panel, for example, a bendable display panel,a foldable display panel, or a rollable display panel.

The window 30 may be the poly(amide-imide) copolymer film and may bedisposed toward an observer side.

The touch screen panel 70 may be disposed to be adjacent to each of thewindow 30 and the display panel 50 to recognize the touched position andthe position change when is touched by a human hand or a materialthrough the window 30 and then to output a touch signal.

The driving module (not shown) may monitor a position where is touchedfrom the output touch signal; recognize an icon marked at the touchedposition; and control to carry out functions corresponding to therecognized icon, and the function performance results are expressed onthe display panel 50.

Another layer may be disposed between the touch screen panel 70 and thewindow 30, and for example, a single layer or plural layers of polymerlayer (not shown) and/or a transparent adhesive layer (not shown) may befurther included.

Another layer may be disposed between the display panel 50 and thewindow 30, and for example, a single layer or plural layers of polymerlayer (not shown) and/or a transparent adhesive layer (not shown) may befurther included.

The display device may be applied to various electronic devices, forexample, a smart phone, a tablet PC, a camera, a touch screen device,but is not limited thereto.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. However, these examples are exemplary, and thescope of the present disclosure is not limited thereto.

Synthesis Example: Synthesis of Poly(amide-imide) Copolymer SynthesisExample 1

Step 1:

700 grams (g) of N,N-dimethyl acetamide as a solvent is placed in around-bottomed flask, 1 mol equivalent (0.127 moles (mol), 40.80 g) of2,2′-bis(trifluoromethyl)benzidine (TFDB) and 2.4 mol equivalent (0.306mol, 21.49 g) of pyridine are dissolved therein, and 50 milliliters (ml)of N,N-dimethyl acetamide is additionally added thereto to completelydissolve TFDB. Subsequently, 0.6 mol equivalent (0.076 mol, 15.52 g) ofterephthaloic dichloride (TPCl) is four times separately added to thesolution at 25° C., and the mixture is vigorously stirred for 15minutes. The resulting solution is stirred under a nitrogen atmospherefor 2 hours, 7 liters (L) of a NaCl solution containing 350 g of NaCl isadded thereto for 10 minutes, and the mixture is additionally stirred.Subsequently, a solid produced therein is filtered and then twiceresuspended and refiltered in 5 L of deionized water. Then, a finalfiltrate on a filter is appropriately pressed to remove remaining waterat maximum and dried at 90° C. under vacuum for 48 hours to obtain anamide oligomer represented by Chemical Formula A. The amide oligomer hasa number average molecular weight of about 997.

Step 2:

20 g (0.02 mol) of the amide oligomer is placed in a 250 ml 4-neckdouble wall reactor equipped with a mechanical stirrer and a nitrogeninlet and preheated at 30° C., and 143 ml of dimethyl acetamide (DMAc)is added thereto.

After stirring the solution at 30° C. under a nitrogen atmosphere, theamide oligomer is completely dissolved, 4.46 g (0.1 mol) of2,2-bis-(3,4-dicarboxylphenyl)hexafluoropropane dianhydride (6FDA) and2.95 g (0.1 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)are slowly added thereto.

Subsequently, 10 ml of dimethyl acetamide (DMAc) is additionally addedthereto to wash remaining BPDA, and the resulting solution is stirredfor 48 hours to obtain a poly(amide-amic acid) copolymer having a solidconcentration of 16%.

Step 3:

100 g of the poly(amide-amic acid) copolymer is placed in a 250 ml4-neck double wall reactor equipped with a mechanical stirrer and anitrogen inlet, 36.29 milligrams (mg) of hexamethylenediisocyanate (2.5mole percent (mol %) based on the total amount of the anhydride) isadded thereto, and the mixture is stirred for 24 hours under a nitrogenatmosphere to obtain a poly(amide-amic acid) copolymer into which across-linking structure is introduced (a poly(amide-imide) copolymerprecursor). Subsequently, 1.76 g of anhydrous acetic acid is addedthereto, the obtained mixture is stirred for 30 minutes, 1.365 g ofpyridine is added thereto, and the obtained mixture is additionallystirred for 24 hours to obtain a poly(amide-imide) copolymer in whichthe cross-linking structure is introduced.

Synthesis Example 2

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for adding 5.0 mol % ofhexamethylenediisocyanate in Step 3 of Synthesis Example 1.

Synthesis Example 3

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for adding 7.5 mol % ofhexamethylenediisocyanate in Step 3 of Synthesis Example 1.

Synthesis Example 4

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for adding 10.0 mol % ofhexamethylenediisocyanate in Step 3 of Synthesis Example 1.

Synthesis Example 5

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for adding 10.0 mol % of toluenediisocyanate instead of the hexamethylenediisocyanate in Step 3 ofSynthesis Example 1.

Synthesis Example 6

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for changing Step 3 of Synthesis Example 1as follows.

Step 3:

100 g of the poly(amide-amic acid) copolymer obtained in Step 2 ofSynthesis Example 1 is placed in a 250 ml 4-neck double wall reactorequipped with a mechanical stirrer and a nitrogen inlet, and dimethylacetamide is added thereto for dilution. Subsequently, 1.2 ml (0.009mol) of triethylamine (TEA) (100 mol % based on the total amount of theanhydride) and 1.29 ml (0.009 mol) of toluene diisocyanate (100 mol %based on the total amount of the anhydride) are added thereto, and theobtained mixture is stirred for 24 hours under a nitrogen atmosphere toobtain a poly(amide-amic acid) copolymer into which a cross-linkingstructure is introduced (a poly(amide-imide) copolymer precursor).

Synthesis Example 7

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 6 except for adding 25 mol % of isophoronediisocyanate (IPDI) instead of the toluene diisocyanate in Step 3 ofSynthesis Example 6.

Synthesis Example 8

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 6 except for adding 50 mol % of isophoronediisocyanate (IPDI) instead of the toluene diisocyanate in Step 3 ofSynthesis Example 6.

Synthesis Example 9

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 6 except for adding 100 mol % of isophoronediisocyanate (IPDI) instead of the toluene diisocyanate in Step 3 ofSynthesis Example 6.

Synthesis Example 10

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 6 except for adding 110 mol % of isophoronediisocyanate (IPDI) instead of the toluene diisocyanate in Step 3 ofSynthesis Example 6.

Comparative Synthesis Example 1

A poly(amide-imide) copolymer is obtained according to the same methodas Synthesis Example 1 except for changing Step 3 of Synthesis Example1.

Step 3:

100 g of the poly(amide-amic acid) copolymer obtained in Step 2 ofSynthesis Example 1 is placed in a 250 ml 4-neck double wall reactorequipped with a mechanical stirrer and a nitrogen inlet, 1.76 g ofanhydrous acetic acid is added thereto, and the mixture is stirred for30 minutes.

Subsequently, 1.365 g of pyridine is added thereto, and the mixture isadditionally stirred for 24 hours to obtain a poly(amide-imide)copolymer.

EXAMPLES Example 1

The poly(amide-imide) copolymer of Synthesis Example 1 is coated on aglass plate and dried on an 80° C. hot plate for one hour, and the glassplate coated with the poly(amide-imide) copolymer is placed in an oven,heat-treated up to 250° C. at 3 degrees Centigrade per minute (°C./min), and slowly cooled down.

Subsequently, the glass plate is removed to form an about 49micrometer-thick (μm-thick) poly(amide-imide) copolymer film.

Example 2

An about 48 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 2 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 3

An about 50 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 3 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 4

An about 52 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 4 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 5

An about 52 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 5 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 6

An about 44 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 7 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 7

An about 47 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 8 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Example 8

An about 52 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Synthesis Example 9 instead of thepoly(amide-imide) copolymer of Synthesis Example 1.

Comparative Example 1

An about 51 μm-thick poly(amide-imide) copolymer film is obtainedaccording to the same method as Example 1, except for using thepoly(amide-imide) copolymer of Comparative Synthesis Example 1 insteadof the poly(amide-imide) copolymer of Synthesis Example 1.

Evaluation

Optical characteristics and mechanical characteristics of thepoly(amide-imide) copolymer films according to Examples 1 to 8 andComparative Example 1 are evaluated.

Film thicknesses of the poly(amide-imide) copolymer films are measuredby using Micrometer (Mitutoyo Corp.).

Light transmittance is measured as Y(D65) in a region of 380 nanometers(nm) to 780 nm by using a UV spectrophotometer (cm-3600d, Konica MinoltaSensing Inc.).

A yellow index (YI) is measured according to an ASTM D1925 standard byusing a UV spectrophotometer (cm-3600d, Konica Minolta Sensing Inc.).

A haze is measured according to an ASTM D1003 standard by using a UVspectrophotometer (cm-3600d, Konica Minolta Sensing Inc.).

A modulus is evaluated by elongating each 10 millimeter-wide (mm-wide)and 50 mm-long film specimens at room temperature at a speed of 5millimeters per minute (mm/min) according to an ASTM D882 standard andthen, measuring five times per sample according to an ASTM D882 standardby using Instron 3365 (Instron Corp.) and obtaining an average.

Viscosity is measured by using Rheometer (RA 550, TA Instruments) at 25°C.

The results are shown in Table 1.

TABLE 1 Light Yellow Viscosity transmittance index Modulus (Pa × s) (%)(YI) Haze (GPa) Example 1 72.7 89.0 2.1 0.4 6.3 Example 2 75.9 89.0 2.20.5 6.3 Example 3 80.2 89.0 2.3 0.4 6.2 Example 4 84.0 89.0 2.1 0.3 6.1Example 5 75.5 88.5 4.2 0.2 6.5 Example 6 55.9 89.0 2.8 0.4 6.0 ± 0.09Example 7 72.5 89.2 2.8 0.5 6.1 ± 0.12 Example 8 57.4 89.4 2.3 0.6 6.5 ±0.12 Comparative 50.0 89.0 2.3 0.4 5.7 Example 1

Referring to Table 1, the poly(amide-imide) copolymer films according toExamples 1 to 8 have equivalent or improved optical characteristics andimproved mechanical properties compared with the poly(amide-imide)copolymer film according to Comparative Example 1.

Accordingly, the poly(amide-imide) copolymers according to Examples 1 to8 show improved mechanical properties due to a cross-linking structureintroduced thereinto.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the present description is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A poly(amide-imide) copolymer, comprising: anamide structural unit comprising an amide bond included in a polymermain chain, and imide structural units comprising an imide bond includedin the polymer main chain, wherein the imide structural units comprise:a first imide structural unit comprising a moiety cross-linked to anadjacent polymer main chain through an amide bond, and a second imidestructural unit, which is not cross-linked to an adjacent polymer mainchain, wherein the first imide structural unit comprises a structuralunit represented by Chemical Formula 1

wherein, in Chemical Formula 1, X is the same or different in eachstructural unit and is independently a substituted or unsubstituted C6to C20 monocyclic aromatic group, a substituted or unsubstituted C4 toC20 monocyclic non-aromatic group, a substituted or unsubstituted C8 toC20 condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 condensed polycyclic non-aromatic group, a substituted orunsubstituted C6 to C20 non-condensed polycyclic aromatic group, asubstituted or unsubstituted C6 to C20 non-condensed polycyclicnon-aromatic group, or a combination thereof, wherein each of thesubstituted or unsubstituted C6 to C20 non-condensed polycyclic aromaticgroup and the substituted or unsubstituted C6 to C20 non-condensedpolycyclic non-aromatic group are linked by a single bond or a linkinggroup comprising a substituted or unsubstituted fluorenyl group, O, S,C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or(CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) are independentlyhydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkyl group, ahalogen, or a hydroxy group, Y is the same or different in eachstructural unit and is independently a substituted or unsubstituted C1to C20 alkylene group, a substituted or unsubstituted C3 to C20cycloalkylene group, a substituted or unsubstituted C3 to C20heterocycloalkylene group, a substituted or unsubstituted C6 to C20arylene group, a substituted or unsubstituted C3 to C20 heteroarylenegroup, or a combination thereof, and R¹¹ is the same or different ineach structural unit and is independently a single bond or a divalentorganic group comprising a substituted or unsubstituted C6 to C30aromatic or non-aromatic ring, wherein the aromatic or non-aromatic ringis present as a single ring; two or more aromatic or non-aromatic ringsare condensed to provide a condensed polycyclic aromatic group; or twoor more aromatic or non-aromatic rings are linked by a single bond or alinking group comprising a substituted or unsubstituted fluorenyl group,O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h),or (CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and * is a linking point of the polymer main chain.
 2. Thepoly(amide-imide)copolymer of claim 1, wherein the structural unitrepresented by Chemical Formula 1 comprises a structural unitrepresented by Chemical Formula 1a;

wherein, in Chemical Formula 1a, R¹⁰ is the same or different in eachstructural unit and is independently a single bond or a linking groupcomprising a fluorenylene group, O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group, Y isthe same or different in each structural unit and is independently asubstituted or unsubstituted C1 to C20 alkylene group, a substituted orunsubstituted C3 to C20 cycloalkylene group, a substituted orunsubstituted C3 to C20 heterocycloalkylene group, a substituted orunsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3to C20 heteroarylene group, or a combination thereof, R¹¹ is the same ordifferent in each structural unit and is independently a single bond ora divalent organic group comprising a substituted or unsubstituted C6 toC30 aromatic or non-aromatic ring, wherein the aromatic or non-aromaticring is present as a single ring; two or more aromatic or non-aromaticrings are condensed to provide a condensed polycyclic aromatic group; ortwo or more aromatic or non-aromatic rings are linked by a single bondor a linking group comprising a substituted or unsubstituted fluorenylgroup, O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH),SiR^(g)R^(h), or (CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensedpolycyclic aromatic group, wherein R^(f) to R^(j) are independentlyhydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkyl group, ahalogen, or a hydroxy group, R¹² and R¹³ are the same or different ineach structural unit and are independently a substituted orunsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C1to C30 haloalkyl group, a substituted or unsubstituted C3 to C30cycloalkyl group, a substituted or unsubstituted C1 to C30 alkoxy group,a substituted or unsubstituted C6 to C30 aryl group, a substituted orunsubstituted C3 to C30 heterocyclic group, a substituted orunsubstituted silyl group, a halogen, a cyano group, a hydroxy group, anitro group, or a combination thereof, n7 and n8 are the same ordifferent in each structural unit and are independently an integerranging from 0 to 3, and * is a linking point of the polymer main chain.3. The poly(amide-imide)copolymer of claim 2, wherein the structuralunit represented by Chemical Formula 1a comprises at least one of astructural unit represented by Chemical Formula 1aa or a structural unitrepresented by Chemical Formula 1ab


4. The poly(amide-imide) copolymer of claim 1, wherein the second imidestructural unit comprises a structural unit represented by ChemicalFormula 3

wherein, in Chemical Formula 3, X is the same or different in eachstructural unit and is independently a substituted or unsubstituted C6to C20 monocyclic aromatic group, a substituted or unsubstituted C4 toC20 monocyclic non-aromatic group, a substituted or unsubstituted C8 toC20 condensed polycyclic aromatic group, a substituted or unsubstitutedC6 to C20 condensed polycyclic non-aromatic group, a substituted orunsubstituted C6 to C20 non-condensed polycyclic aromatic group, asubstituted or unsubstituted C6 to C20 non-condensed polycyclicnon-aromatic group, or a combination thereof, wherein each of thesubstituted or unsubstituted C6 to C20 non-condensed polycyclic aromaticgroup and the substituted or unsubstituted C6 to C20 non-condensedpolycyclic non-aromatic group are linked by a single bond or a linkinggroup comprising a substituted or unsubstituted fluorenyl group, O, S,C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or(CR^(d)R^(e))_(p) (1≤p≤10), wherein R^(a) to R^(e) are independentlyhydrogen, a C1 to C30 alkyl group, a C1 to C30 haloalkyl group, ahalogen, or a hydroxy group, R¹¹ is the same or different in eachstructural unit and is independently a single bond or a divalent organicgroup comprising a substituted or unsubstituted C6 to C30 aromatic ornon-aromatic ring, wherein the aromatic or non-aromatic ring is presentas a single ring; two or more aromatic or non-aromatic rings arecondensed to provide a condensed polycyclic aromatic group; or two ormore aromatic or non-aromatic rings are linked by a single bond or alinking group comprising a substituted or unsubstituted fluorenyl group,O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(f)(OH), SiR^(g)R^(h),or (CR^(i)R^(j))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic group, wherein R^(f) to R^(j) are independently hydrogen, a C1to C30 alkyl group, a C1 to C30 haloalkyl group, a halogen, or a hydroxygroup, and * is a linking point of the polymer main chain.
 5. Thepoly(amide-imide) copolymer of claim 4, wherein the second imidestructural unit comprises a structural unit represented by ChemicalFormula 3a:

wherein, in Chemical Formula 3a, R¹⁰ is the same or different in eachstructural unit and is independently a single bond or a linking groupcomprising a fluorenylene group, O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(b)R^(c), or (CR^(d)R^(e))_(p) (1≤p≤10),wherein R^(a) to R^(e) are independently hydrogen, a C1 to C30 alkylgroup, a C1 to C30 haloalkyl group, a halogen, or a hydroxy group, R¹¹is the same or different in each structural unit and is independently asingle bond or a divalent organic group comprising a substituted orunsubstituted C6 to C30 aromatic or non-aromatic ring, wherein thearomatic or non-aromatic ring is present as a single ring; two or morearomatic or non-aromatic rings are condensed to provide a condensedpolycyclic aromatic group; or two or more aromatic or non-aromatic ringsare linked by a single bond or a linking group comprising a substitutedor unsubstituted fluorenyl group, O, S, C(═O), OC(═O), S(═O), S(═O)₂,C(═O)NH, CR^(a)(OH), SiR^(g)R^(h), or (CR^(i)R^(j))_(p) (1≤p≤10) toprovide a non-condensed polycyclic aromatic group, wherein R^(f) toR^(j) are independently hydrogen, a C1 to C30 alkyl group, a C1 to C30haloalkyl group, a halogen, or a hydroxy group, R¹² and R¹³ are the sameor different in each structural unit and are independently a substitutedor unsubstituted C1 to C30 alkyl group, a substituted or unsubstitutedC1 to C30 haloalkyl group, a substituted or unsubstituted C3 to C30cycloalkyl group, a substituted or unsubstituted C1 to C30 alkoxy group,a substituted or unsubstituted C6 to C30 aryl group, a substituted orunsubstituted C3 to C30 heterocyclic group, a substituted orunsubstituted silyl group, a halogen, a cyano group, a hydroxy group, anitro group, or a combination thereof, n7 and n8 are the same ordifferent in each structural unit and are independently an integerranging from 0 to 3, and * is a linking point of the polymer main chain.6. The poly(amide-imide) copolymer of claim 5, wherein the second imidestructural unit comprises at least one of a structural unit representedby Chemical Formula 3aa or a structural unit represented by ChemicalFormula 3ab:

wherein, in Chemical Formulae 3aa and 3ab, * is a linking point of thepolymer main chain.
 7. The poly(amide-imide) copolymer of claim 1,wherein the amide structural unit comprises a structural unitrepresented by Chemical Formula 4:

wherein, in Chemical Formula 4, L is the same or different in eachstructural unit and is independently a single bond, —CONH—, -Ph-CONH-Ph-or —NHCO-Ph-CONH—, wherein “Ph” is a substituted or unsubstitutedphenylene group, R² is the same or different in each structural unit andis independently a divalent organic group comprising a substituted orunsubstituted C6 to C30 aromatic or non-aromatic ring, wherein thearomatic or non-aromatic ring is present as a single ring; two or morearomatic or non-aromatic rings are condensed to provide a condensedpolycyclic aromatic or condensed polycyclic non-aromatic group; or twoor more aromatic or non-aromatic rings are linked by a single bond or alinking group comprising a substituted or unsubstituted fluorenyl group,O, S, C(═O), OC(═O), S(═O), S(═O)₂, C(═O)NH, CR^(k)(OH), SiR^(l)R^(m),or (CR^(n)R^(o))_(p) (1≤p≤10) to provide a non-condensed polycyclicaromatic or non-condensed polycyclic non-aromatic group, wherein R^(k)to R^(o) are independently hydrogen, a C1 to C30 alkyl group, a C1 toC30 haloalkyl group, a halogen, or a hydroxy group, R⁶ to R⁹ are thesame or different in each structural unit and are independently asubstituted or unsubstituted C1 to C30 alkyl group, a substituted orunsubstituted C1 to C30 haloalkyl group, a substituted or unsubstitutedC3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30alkoxy group, a substituted or unsubstituted C6 to C30 aryl group, asubstituted or unsubstituted C3 to C30 heterocyclic group, a substitutedor unsubstituted silyl group, a halogen, a cyano group, a hydroxy group,a nitro group, or a combination thereof, n3 and n4 is the same ordifferent in each structural unit and is independently an integerranging from 0 to 4, n5 and n6 are the same or different in eachstructural unit and are independently an integer ranging from 0 to 3,n3+n5 is the same or different in each structural unit and isindependently an integer ranging from 0 to 4, n4+n6 is the same ordifferent in each structural unit and is independently an integerranging from 0 to 4, and * is a linking point of the polymer main chain.8. The poly(amide-imide) copolymer of claim 7, wherein the amidestructural unit comprises at least one of a structural unit representedby Chemical Formula 4a or a structural unit represented by ChemicalFormula 4b;

wherein, in Chemical Formulae 4a and 4b, * is a linking point of thepolymer main chain.
 9. A poly(amide-imide) copolymer film comprising thepoly(amide-imide) copolymer of claim
 1. 10. The poly(amide-imide)copolymer film of claim 9, wherein the poly(amide-imide) copolymer filmhas a modulus of greater than or equal to about 5.8 gigapascals.
 11. Thepoly(amide-imide) copolymer film of claim 10, wherein thepoly(amide-imide) copolymer film has a light transmittance of greaterthan or equal to about 80% and a yellow index of less than or equal toabout 4.5.
 12. A window for a display device comprising thepoly(amide-imide) copolymer film of claim
 9. 13. A display devicecomprising the window for a display device of claim
 12. 14. A displaydevice comprising the poly(amide-imide) copolymer film of claim 9.